The present invention relates generally to laboratory work cabinets such as exhaust hoods, fume hoods, and biological safety cabinets and, more particularly, to means for the mounting, installation and removal of contaminant filters in such cabinets.
Various forms of work cabinets are commonly utilized in laboratories in many diverse industries ranging from educational and research institutions to chemical, medical and pharmaceutical concerns. Such cabinets may include, for example, fume hoods, other exhaust hoods, and biological safety cabinets. While such cabinets may differ in varying structural and operational respects, the common purpose and use of such cabinets is to provide scientists and associated personnel with access to a work chamber for performing various scientific tests, reactions, experiments and like operations while protecting the operator and the ambient laboratory environment from exposure to potentially dangerous contaminants.
All such cabinets necessarily include an air circulation system for controlling airflow within the cabinet and for filtering contaminants from the airflow. In turn, all such cabinets have the periodic need to replace air filters as they become loaded with accumulated filtered materials. In some cabinets, the removal and replacement of contaminant laden filters can be a time consuming process involving extended downtime in the normal operation of the cabinets. In biological safety cabinets which provide a biohazard containment means which enables laboratory personnel to perform various procedures utilizing biologically hazardous substances while protecting the personnel, the work product and the ambient environment from exposure to and contamination by such substances, that issue is particularly prevalent because such cabinets typically include two filters requiring periodic replacement, one for filtering air recirculating within the cabinet and another for filtering air being exhausted from the cabinet, and because each of the filters must be installed with highly secure seals to protect against the dangerous biologically hazardous substances typically being handled.
Thus, while the present invention is applicable to the mounting, installation, removal and replacement of filters in virtually any laboratory work cabinet, the present invention is particularly applicable to biological safety cabinets. For example, one class of biological safety cabinet referred to as Class II, Type A2 cabinets basically have a work chamber that is mostly enclosed except for a front access opening sufficient for a user's hands to perform procedures within the work chamber. An air circulation system maintains a continuously circulating positive air flow within the work chamber which is controlled to move laminarly in parallel relation to the front access opening to prevent escape of the internal cabinet air outwardly through the forward access opening to protect the user and the ambient area from contamination. The air circulation system utilizes a fan to continuously withdraw air from the work chamber into an adjacent filtration chamber from which a portion of the air is recirculated into the work chamber through a first high efficiency particulate air filter, commonly referred to as a HEPA filter, while the balance of the withdrawn air is exhausted outside the cabinet through a second HEPA filter. Typically, a ratio of about 70% recirculated air to 30% exhausted air is maintained in Class II A2 cabinets. The exhausted air is replaced by ambient air from the surrounding room drawn first into the filtration chamber before entering the work chamber through the first filter, thereby to prevent room air contamination of the work chamber and also to maintain the integrity of the laminar air flow along the front access opening.
It is important that the full perimeter of each filter in such biological safety cabinets be securely sealed to prevent any portion of the recirculating or exhausting airstreams from bypassing the filters and thereby contaminating either the work chamber or the exhausted air with biological materials. It is equally important that the filters in such biological safety cabinets be replaced with sufficient frequency to maintain uniformity in the laminar velocity of the circulating air and to minimize airborne contaminants in the circulating air. In turn, therefore, it is desirable that downtime in operation of the cabinets be minimized when accomplishing filter replacement but that objective is outweighed by the necessity that filters be installed precisely with secure perimeter seals. Hence, there is a continuing need in the industry for a simple and quick yet reliable means of removing and replacing filters in such cabinets.